Although catalysts that include nickel metal Ni(0) and nickel-binding ligands have been employed for a number of years, procedures for making those catalysts are not optimally efficient. Nickel metal atoms can be combined with phosphorus-containing ligands to generate hydrocyanation catalysts (see, e.g., U.S. Pat. Nos. 5,981,722, 7,629,484 and 7,470,805) but not always with optimal results. Nickel is poorly soluble, and many nickel metal preparations are unsuitable for use in catalysts because nickel metal is not bound to their ligands. For example, when nickel metal is agglomerated, poorly reduced, or impurities are present, low levels of nickel combine with phosphorus-containing ligands and only small amounts of catalyst are formed. Moreover, nickel starting materials from different commercial sources can have different properties, and even when processed identically one source can provide nickel metal that can combine well with phosphorus-containing ligands, while another source does not.
The processing of nickel source material towards producing active nickel is a difficult process because fine particle sizes of the reduced nickel are desired, but such fine particles are often cohesive. Also sintering of nickel particles occurs at temperatures as low as 200° C. (P. Compo et. al., Powder Technology, 51: 85-101 (1987); B. B. Panigrahi et. al., Science of Sintering, 39: 25-29 (2007)). Reduction of nickel is described in several references, such as U.S. Pat. Nos. 3,793,005, 3,656,934, 2,000,171 and Rhamdhani et. al., Proc. Eur. Metal. Conf. pp. 899-913 (2009). However, such processes do not provide optimal nickel metal particles for making nickel catalysts due to impurities, particle agglomeration, high temperatures employed during reduction, and other factors.
Production of active nickel in a fluidized bed reactor requires additional steps and careful monitoring to minimize this sintering and agglomeration phenomena due to cohesive forces of attraction between particles. This has previously been accomplished by adding some amount of steam to the process (see, earlier filed U.S. Patent No. 20130144079) and by adjusting other variables. There are several limitations to the fluidized bed/steam processing technique that undermine its utility, such as the low amounts of hydrogen that can be utilized when steam is present, and the quality of nickel produced due to presence of steam.
More efficient processes for making such catalysts are desirable, so that greater percentages of nickel preparations can be used in nickel-ligand catalysts and so that less waste is generated during catalyst preparation.